The invention relates to a device for determining the start of injection in a direct-injection internal combustion engine. It is important in a direct-injection internal combustion engine to know the exact start of injection in order to be able to make an optimum setting of the injection profile and thus also of the combustion behavior.
This holds, in particular, for the injection systems known under the designation of common rail systems in diesel engines and under the designation of high-pressure direct-injection systems in spark-ignition engines. In such systems a high-pressure pump is used to convey fuel from a fuel reservoir into a high-pressure accumulator via which the fuel is then present at injection valves which are disposed in the combustion chambers of the internal combustion engine. The processes of injecting into the combustion chambers of the internal combustion engine are initiated by applying current to the injection valves, the start of injection into the combustion chambers depends on the response delay of the injection valves and on the pressure present at the injection valves.
Various methods are already known in the prior art for determining the exact start of injection into the combustion chambers of the internal combustion engine after current has been applied to the injection valves, and in order to be able thereby to make an optimum setting of the injection profile and/or combustion profile in the combustion chamber. Thus, it has been proposed to fix the exact start of injection in accordance with the respective operating conditions of the internal combustion engine with the aid of a characteristic diagram stored in the control unit of the internal combustion engine. However, in this case it is necessary in advance for the characteristic diagram data to be determined either by simulation calculation or by experiment, something that is very expensive since it has to be performed separately for each type of injection system. Even after the characteristic diagram data have been matched to the respective type of injection system, strong deviations still frequently occur between the start of injection as determined from the characteristic diagram data and the actual start of injection into the combustion chamber. It is also the case in the prior art that pickups, which directly scan the stroking of the nozzle needle in the injection valve in order to avoid these disadvantages of an evaluation based on characteristic diagram data, are already known. However, these pickups are relatively complicated and expensive, since they have to be installed directly into the injection valves.
It is accordingly an object of the invention to provide a device and method for determining the start of injection in a direct-injection internal combustion engine which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which is distinguished by simple construction and high reliability and measuring accuracy.
With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with a direct-injected internal combustion engine having an injection valve and an injection line connected to the injection valve, a device for determining a start of injection in the direct-injection internal combustion engine, including: a magnetoelastic pressure sensor disposed on the injection line connected to the injection valve, the magnetoelastic pressure sensor detecting a magnetoelastic effect caused by a pressure change in the injection line owing to an injection process of the injection valve and outputting a measurement signal for determining the start of injection.
The device according to the invention essentially has a pressure sensor which is disposed directly at the injection line to the injection valve and uses the magnetoelastic effect to detect the pressure change triggered by the injection process in the injection line. The measurement signal of the pressure sensor which indicates such a pressure change is temporally correlated in an evaluation unit for the purpose of initiating the injection process, in order to determine a dead time between the initiation of the injection process and the start of injection. The device according to the invention is distinguished by a simple and cost effective configuration which, in addition, can easily be integrated in any type of injection system. Furthermore, determining the start of injection requires only very simple detection and evaluation of the measured values.
It is advantageous, in particular, for the magnetoelastic pressure sensor to be constructed as a coil which is made from a ferromagnetic material and is wound around the injection line. The pressure sensor construction is particularly simple, robust and cost effective.
In accordance with an added feature of the invention, there is an evaluation device receiving and temporally correlating the measurement signal of the magnetoelastic pressure sensor with a drive signal output to the injection valve for initiating the injection process to determine a dead time between an initiation of the injection process and the start of injection.
In accordance with an additional feature of the invention, the magnetoelastic pressure sensor is formed of a ferromagnetic material.
In accordance with another feature of the invention, the magnetoelastic pressure sensor is formed of a nickel-iron alloy with a nickel component of 80%.
In accordance with a further added feature of the invention, the magnetoelastic pressure sensor has a coil wound around the injection line to detect a voltage induced by the pressure change in the injection line.
In accordance with a further additional feature of the invention, the magnetoelastic pressure sensor has a transformer with two coils detecting a voltage induced by the pressure change in the injection line.
In accordance with yet another feature of the invention, the evaluation device corrects an interference component generated by the drive signal of the injection valve in the measurement signal of the magnetoelastic pressure sensor resulting in a corrected measurement signal.
In accordance with another added feature of the invention, the evaluation device determines the measurement signal of the magnetoelastic pressure sensor by deriving a difference between an initial measurement signal and a signal picked up by the magnetoelastic pressure sensor in a time period between the drive signal of the injection valve and an instant of the start of injection that is yielded by a response delay of the injection valve.
In accordance with another additional feature of the invention, the evaluation unit compares an absolute value of the corrected measurement signal with a threshold value to determine the start of injection of the injection valve in an event of overshooting of the threshold value.
In accordance with a concomitant feature of the invention, the evaluation device indicates the start of injection of the injection valve only if an absolute value of a predetermined sequential number of sample points of the measurement signal overshoot the threshold value.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and method for determining the start of injection in a direct-injection internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.